Jackson Browne is poised to descend on us in two forms this month, with two concerts on Friday at the Capitol Theater in Passaic, N.J., and four on Saturday and next Sunday at the Palladium on 14th Street, and with his eagerly awaited new record, "The Pretender," due out in a couple of weeks.

Mr. Browne is a most interesting artist all by himself. But he is also significant as perhaps the most representative major singer/songwriter of a genre of Los Angeles country-folk-rock, and his imminent double arrival sets one to thinking about his context. Mr. Browne, of course, is particularly Californian, since his great-grandfather established the Browne family in the region. But other Los Angelenos, many of them Californians by adoption, ride high on the charts and in the affections of millions of American pop-music fans these days - artists such as the Eagles, Linda Ronstadt and Neil Young. And what might be called the Los Angeles school also includes a host of lesser lights, like Chris Hillman, John David Souther, Andrew Gold and Dan Fogelberg, who have practiced the Los Angeles idiom for a greater or lesser period of time but who haven't been able to bend it to consistently expressive personal uses.

The best talents of this genre are still turning out music of undoubted excellence. But it's hard to avoid the thought, especially while sitting through sets by the others that Los Angeles rock as we've known it over the past eight years may be heading comfortably downhill. All those carefully clipped beards and that clean-cut urban cowboy attire are only a visual symbol of the tasteful pall that blankets this music - tastefulness that ultimately precludes spontaneity of feeling, and overlays the inherent vitality of the music with packaged slickness.

Some will simply disagree with this notion, and they can legitimately point to the latest disks of Miss Ronstadt and Mr. Young to bolster their convictions. And possibly for any such criticism to be taken seriously it would have to come from Los Angeles itself; as Los Angeles solidifies its claim as the country's pop-music capital, New Yorkers become increasingly vulnerable to a charge of sour grapes.

Others might plausibly argue that any attempt to scoop "Los Angeles rock" into an analytical bag keeps leaking messily at the seams. What do you do about the myriad country-folk-rockers who don't live in Los Angeles? What about the many other pop musicians native and imported, who live in the area and don't conform to the prevailing stereotype? There are homegrown progressives like Frank Zappa, Captain Beefheart and the Mael Brothers. There are loners like Bob Dylan, Dory Previn and Randy Newman. There are jazzy ex-folkies like Joni Mitchell and Maria Muldaur. There are English rockers like Rod Stewart and Ringo Starr. Or adult schlock-pop performers and teenybopper idols like Herb Alpert, Tony Orlando and Paul Williams and the Osmonds and John Travolta. There are black artists, like Diana Ross, Curtis Mayfield and Smokey Robinson and the rest of the Motown family. There are middle-of-the-roaders like the Captain and Tenille, Cher, Neil Diamond, Olivia Newton-John and Helen Reddy. There are flashy punk fantasies like the Runaways. And on into the smog-filled, eerily glowing Hollywood night.

Still, when one thinks of "Los Angeles rock" one thinks first of Mr. Browne, Miss Ronstadt, the Eagles, Crosby, Stills, Nash and Young together and separately, the Gram Parsons-influenced Byrds and their successors and maybe Warren Zevon. And one thinks of the bands that preceded them and in some senses paved their way: the other slick folk-revival groups of the early 60's that helped prepare us for the early Byrds; the Beach Boys, Phil Spector, and the Mamas and the Papas for their celebrations of personal pleasure and their symphonic, densely harmonized textural effects; and the Doors for their artsy explorations of the darker side of all this sunny dreaming.

The links between the present-day members of this Los Angeles rock constituency can be traced in a number of ways. The fan magazines continually report on their presence at one another's parties and openings. They collaborate on songs and sing backup for one another. They use the same producers, session men and recording studios. They hang out at the same clubs (there isn't the variety of trendy places that New York offers so effortlessly). Many of them have found refuge on the same record label, Asylum, and several were or used to be managed by Elliott Roberts, who used to be a partner of David Geffen, who founded Asylum.

They even often belong at one point or another to the same bands. Most of the American and British pop magazines have at one time or another published family trees of the various L.A.-rock interminglings, and they all reveal a nest of personal and professional bonds that make Peyton Place look positively puritanical. Mr. Hillman's career highlights, from the Byrds to the Flying Burrito Brothers to Mananas [sic] to Souther-Hillman-Furay, give some idea. The Eagles (or most of them) used to be Miss Ronstadt's backup band; Mr. Gold leads her current one. David Crosby was in the Byrds, then worked with Joni Mitchell and then joined Crosby, Stills and Nash (which then took on Neil Young). Bernie Leadon played with Miss Ronstadt before the other Eagles and then was in Dillard and Clark and the Burrito Brothers before the Eagles got together as such. Firefall has emerged recently as a repository of ex-Byrds and Burrito Brothers. Mr. Zevon is a protégé of Mr. Browne. And so forth.

But the best and most meaningful way to establish a category of Los Angeles rock is to explore the conceptual themes it shares in its lyrics and the musical similarities in its sound. Naturally not everybody is concerned with precisely the same themes. Mr. Browne has dealt with an intensely private romanticism, one that seeks another (as in "Looking into You") or into solitude ("Rock Me on the Water," quoted above). He is a man who has lived through the more buoyant and communal 1960's and found them no longer meaningful. In his later albums especially, the image of an impending apocalypse - huge, fearful and incapable of control yet ultimately cleansing - looms ever larger. Images of water and the sea predominate in his work - as if the surfer escapism of a decade ago has been transformed into cosmic transcendence.

Miss Ronstadt is the primary present-day priestess of love. Love - sexual or romantic, winning or losing - is the basis of most pop music to be sure. But Miss Ronstadt's choice of songs (and those she has begun to write herself, on her latest album) concentrates on love with a single-mindedness that sets her apart. Sometimes she is successful in her amorous pursuits. More commonly she is in despair, and her ability to project believability in her laments is the key to her FM success.

The Eagles, especially in their more ambitious earlier albums, dealt with the classic American cowboy outlaw image as a metaphor for loneliness. The other members of CSN&Y have fallen back mostly onto a particularly callow sort of love song or childlike, naive political messagizing. But Neil Young - who lives south of San Francisco but who in every way must be considered part of the Los Angeles pantheon - continues as one of the real and distinctive giants of contemporary popular music, with his desperate, searching examinations of the self.

What joins these artists together on a thematic level is indeed this very unabashed self-absorption. Some of them may do political benefits or sing occasional songs about other subjects. But the center of their art is an adult exploration of the same themes that in more banal form dominated AM radio in Southern California (and America) in the early-mid 1960's. These are aging white hippies, tinged with Hollywood glamor. They have made a good deal of money and can afford life styles that insulate them from the more harsh urban realities of the rest of the country. They are escapists whose perception of their moral detachment only serves to lend their isolation a minor-key coloration. Mr. Browne is particularly interesting in this regard because of his delicate blend of participation in and disengagement from such sentiments. Joni Mitchell - who shares every attribute of the circle except the country-tinged musical idiom - is a particularly acute instance of self-involvement. Even Mr. Zevon, who has attracted a good deal of favorable attention outside Los Angeles for his often mordant view of his home, is still very much a part of it, trapped in an endless smalltown round of private concerns and social interactions even as he protests it.

Musically, too, these artists have their differences. Miss Ronstadt's throbbing, rich voice is unmatched by any of the others, and her ability to express Romantic yearning in phrasing and inflection is unique. The Eagles offer affecting harmonizing (when they aren't trying to be heavy-duty rock-and-rollers). CSN & Y at its best had a nervous energy closer to Miss Mitchell than the Eagles. Mr. Young's quavering tenor is a classic instance of a voice that communicates all the more intensely through its technical imperfections.

Underlying most of this, however, is a plodding reliance on a set of stylistic signatures that has become all too familiar: the electric guitars picking out countryish melodies above the strumming acoustic guitars; the weepy minor keys; the clean-cut thumping regularity of the drums; the antiseptic studio atmosphere; and above all those droopy pedal steel guitars, slithering through it all. What is ironic is that a country-folk-rock sound, back when Gram Parsons pioneered its use with the Byrds, was an intensely natural antithesis to slick rock, pop and soul. People used this instrumentation to express organic, back-to-nature sentiments. But when everybody started being organic at the same time, the music fell into a set of clichés so pervasive as to preclude any hint of naturalness. Too much of this music, whatever the interest of the lyrics, sounds simply repetitious.

It's easy, probably too easy, to take a superior attitude toward all of this, and a number of Eastern, Midwestern and Northern California rock writers have done just that. They usually have a few kind words to say for Mr. Browne, and most of them love Mr. Young. But the rest seems to them facile and depersonalized. Indeed the two principal dangers that this musical style faces are slickness and detachment from the country as a whole. Los Angeles is the center of the television industry, after all, and of plastic popular entertainment in several other media. There is a continual tendency to reduce art to a level that will sell in neatly uncontroversial form. Even as the Los Angeles rock musicians think they are battling against such creeping cynicism they succumb to it. The effects on Carole King and Mr. Dylan when they moved to Los Angeles are not encouraging. And in his excellent "Star-Making Machinery," Geoffrey Stokes describes the tension between Commander Cody and His Lost Planet Airmen - who espoused a musical style akin to the Los Angelenos - and John Boylan, who had been brought in to produce their album. Mr. Boylan, a staple on the Los Angeles music scene and the former producer of Miss Ronstadt, never could quite convince the Ann Arbor and San Francisco radicals in the band that a clean, accurate sound was in their best interests. And they were right.

The detachment from the rest of the country comes from Los Angeles's climate, sociology and status as the enbodiment [sic] of the all-American dream. In Los Angeles, one lives in enclaves apart from one's potentially disagreeable neighbors. Like-minded communities are enclaves, and the grander houses are too, safe behind their walls. Partly as a result Los Angeles rock is about the most determinedly white, educated and self-consciously sensitive pop music we have. The driving urgency of the ghetto or the barrio finds few echoes here, and the earthy intensity of traditional country music is even more completely purged than it is in modern-day Nashville.

But that's not necessarily all bad. White, college-educated people who listen to FM radio and derive their deepest artistic experience from Jackson Browne and Neil Young shouldn't be dismissed as fools. Limited, maybe, but not reprehensible. It should be perfectly possible to appreciate the best in Los Angeles rock without condoning the worst or shutting one's ears to other kinds of music. And maybe even the predictions of decline are premature. After all, Mr. Browne and Mr. Young and Mr. Zevon and Miss Ronstadt and many others are still making music that can give deep satisfaction. As long as they keep on touching us, their tradition of Los Angeles rock will still be very much alive.